As the semiconductor industry continues to grow, the need to develop increasingly complex integrated circuits with smaller feature sizes and dimensions has been highly sought after. Driven by the demand for high performance, integrated circuit (IC) devices have been incorporating more circuits per unit area. However, this may also create a significant challenge in creating reliable interconnect structures in order to support device scaling and higher operating speeds for future generations of integrated circuit devices.
Conductive pillars are generally used in small IC packages with relatively high input-output (IO) density. Typically, solder is used to connect the conductive pillars on an IC die to conductive pads on a package substrate. A reflow process can be performed to melt the solder, which forms solder joints between the conductive pillars and conductive pads after the molten solder is cooled. However, problems may also occur when solder is used in the IC packages. For example, it is difficult to prevent the solder from wetting to the sidewalls of the conductive pillars, which may cause bridging between adjacent conductive pillars. To avoid solder wetting, the conductive pillars need to be placed adequately far apart from each other (e.g., at least 50 micrometers apart), which limits the density of an IC package.
For the case of pre-soldered bumps on a package substrate, thermal compression bonding may be performed to attach the conductive pillars on the IC die to the pre-soldered bumps on the package substrate. When the pre-solder bumps fuses together with the adjacent conductive pillars and conductive pads during the thermal compression bonding process, solder bridging may occur when the conductive pillars and pads are too close to one another. This may cause inadvertent shorting of the solder bumps in the IC package.